Formula v-bottom designs

Discussion in 'Boat Design' started by sideskraft, Oct 16, 2015.

  1. sideskraft
    Joined: Oct 2015
    Posts: 1
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    Location: West Michigan

    sideskraft Lake Michigan Wave Basher

    A few years ago I purchased my first Thunderbird boat -- an '84 Formula F3LS (21.5ft) with a single 260 Merc stern drive. I purchased it with the intent of boating along the east shore of Lake Michigan (we live north of Holland). Although it handles waves well for its size, it quickly became apparent that we needed something larger, since the typical conditions in this area feature 3+ foot waves.

    Soon after I began the search for a larger classic Formula, and focused on the 233 Interceptor (looked at a few in the Midwest). Ultimately I purchased an '81 Formula 255 Liberator with twin 260 Merc/Alpha drives. I was drawn to its enormous cabin, deep-v hull design and prodigious freeboard, which would help keep the wife at ease in big water. I only had it in the water for 15 minutes when I ran into some electrical issues. I've completely renovated the cabin (almost done) and have gone through most of the boat to get her ship shape. All the posts I'd read about Formula boats is that they have one of the softest rides of all boat designs.

    My reason for writing to you is that I'm interested in learning about the 255 hull design objectives, and how it compares in speed, handling and "wave cutting" compared to other Formula boat designs, such as the legendary 233. I'm hoping that some of this forum's members understand the physics of boat hull designs, particularly the deep-v bottom and its wave handling properties.

    Looking at the attached pics, you can see that the 255 (blue boat) has a shallower "entry angle" than the 233 Formula (white) -- I'll call it less trawler-like. At the rear of the boat, the 255 bottom becomes somewhat rounded. The 233 has a deeper and steeper v (and also rounded), and it appears to have a deeper v at the front entry as well. The F3LS (red) has a sharp v at the transom and a slightly more "aggressive" entry than the 255. The sharp v at the transom was used on all Formula bottoms beginning in 1984 (the 255 retired in '82 and the 233 in '83). I discovered that, although the Liberator model was introduced in '79, the first 255 came out in '76 as an "open cruiser", so its original design intent was likely a compromise between ride, stability, performance and efficiency. It appears that Formula kept the original 255 hull bottom for the Liberator model.

    What impacts result from the "sleeker" front attack angle of the 255 compared to the 233 (and to a lesser extent the F3)? Frankly my "non-engineer" impression is that the 233 front end will do better at stuffing avoidance than the 255. The 255 overall hull design looks to me to be rear heavy -- if it had a beefier front end (like the 233) I think it would look more balanced IMO. The front of the 233 sits up high, similar to most high performance offshore boats, whereas the 255 is closer to being level.

    What impacts result from the 255's rounded keel at the transom compared to the sharp v of the 272 and F3 and the deeper round-v of the 233? I'm concerned that, even though the 255 has a sharp v at the front, the more round bottom at the transom will cause pounding. I haven't measure the angle of the 255 at the transom, but it's definitely less than the 233, which I believe is 24 degrees -- maybe the 255 is 20 degrees?

    The 233 is known for it's "rocker" in the rear, which as I understand allows the bow to ride up higher to reduce hull surface drag. It's clear that my 255 has no rocker, so I wonder what the pluses and minuses are of that design.

    I believe that Jim Wynn designed the 233 in the early 60s, and John Adams designed the 255/272/F3 which were probably influenced by the 233.

    My hope is that my 255 will provide a reasonably soft and dry ride in Lake MI at planing speeds in waves up to 4 feet. It weighs 5600lb dry, so with some fuel, gear and a couple people it's likely displacing at least 6500lb.

    Any input you can provide will be greatly appreciated -- thanks for your time.

    Attached Files:

  2. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    Seeing you have already purchased the boat and done a bit of work on it, you will just have to "suck it and see" to determine whether it meets your expectations. I'd expect the later Formula hulls sit better at rest than a 233, which was a bit tender. That would come from a reduced deadrise angle, mainly. It is also possible they can hold plane at a lower speed than a 233, which would be an asset. Any of those boats should give satisfactory service in conditions you would want to be out there in, in the first place.
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